Card manufacturing technique and resulting card

ABSTRACT

A card manufacturing technique and the resulting card are provided. The card has a ground and/or power layer extending to the edges of a circuit board for electrostatic discharge protection but also has gaps at the edge of the ground and/or power layer to avoid short circuiting with conductive segments of another layer deformed when the card is trimmed during manufacture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/456,077, filed Jun. 6, 2003, which in turn is a divisional of U.S.application Ser. No. 09/921,664, filed Aug. 3, 2001, now U.S. Pat. No.6,597,061, which applications are hereby incorporated by reference intheir entirety.

The present application is related to U.S. application Ser. No.09/096,140 issued as U.S. Pat. No. 6,040,622 which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates generally to circuit boards, a method of making amemory card integrating a circuit board, and the resulting memory card.

BACKGROUND OF THE INVENTION

This invention relates generally to circuit boards, and morespecifically to circuit boards of memory cards utilized in portabledevices to store data. Although the invention has application to a widevariety of circuit boards, it is described herein to be implemented in amemory card, specifically a portable memory card having flashelectrically-erasable and programmable read-only memory (flash EEPROM).

In recent years, devices such as digital cameras, digital audio players,and personal digital assistants have become popular. These devicesrequire a large amount of storage capacity in a small and ruggedpackage. Memory cards utilizing high density non-volatile memory arefrequently inserted and removed from these devices and printers orexternal readers attached to personal computers. The frequent handlingof these cards results in a high risk of electrostatic discharge.

Thus, it is desired to have a small thin memory card that is immune fromelectrostatic discharge yet simple to manufacture and assemble.

SUMMARY OF THE INVENTION

Memory cards are getting smaller and thinner, yet the capacity isincreasing and they are also becoming more densely packaged. Frequenthandling of these cards results in a high risk of electrostaticdischarge (ESD).

A memory card and a method of making a memory card resistant to damagefrom electrostatic discharge and less prone to short circuiting of themultiple conductive layers of the card is described. The memory card isformed by encapsulating or placing a circuit board into a plastic cover.At a junction between the plastic cover and an edge of the circuit boardthere is a gap where an electrostatic discharge is prone to enter anddamage the circuit components of the memory card. The ground and powerlayer extend to the edge of the circuit board and along the junctionbetween the circuit board and the memory card. Thus any electrostaticdischarge is absorbed by either of these layers and damage to the othercircuit components from the high voltage discharge is avoided. A priormethod of avoiding short circuits due to the trimming process involvedpulling back the entire edge of the conductive layer away from the edgeof the circuit board, however this method affords little if any ESDprotection to the susceptible components of the memory card.

During the manufacturing of the memory card, the circuit board istrimmed to its final dimensions. Conductive segments of a metallic layerthat are located at the edge of the circuit board are deformed duringthe trimming process and can extend over an insulating layer and contacta second metallic layer, in this case either the ground or power layer,thus resulting a short circuit. As previously mentioned, it is desirousto extend the ground and/or power layer to the junction of the card forelectrostatic discharge purposes. Therefore, in order to avoid shortcircuiting yet preserve maximum ESD protection, small gaps are formed atthe edge of the second conductive layer that are vertically aligned withthe conductive segments such that any deformation that may occur duringthe trimming process will not result in a short circuit. The deformationof the conductive segments will fall into the gap at the edge of thesecond conductive layer rather than making contact with the layer. Thesize of the gaps is small in relation to the remaining edge of theground and/or power layer at the junction of the circuit board and thecover, thus ensuring a high level of ESD protection while avoiding shortcircuits from the trimming of the board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the memory card exemplifying the presentinvention.

FIG. 2 is a cross-sectional view of the memory card exemplifying thepresent invention.

FIG. 3 is a perspective exploded view showing the conductive layers ofthe card.

FIG. 4 is a perspective exploded view showing the conductive layers ofthe card during manufacturing.

FIG. 5 a is an enlarged perspective view of an edge of the memory card.

FIG. 5 b is an enlarged perspective view of another example of an edgeof the memory card.

FIG. 5 c is an enlarged perspective view of another example of an edgeof the memory card.

FIG. 6 a is a cross-sectional view along section A—A of the card shownin FIGS. 4 and 5 a.

FIG. 6 b is a cross-sectional view along section A—A of the card shownin FIGS. 4 and 5 c.

FIG. 7 is a top view of a gap of FIGS. 3–5.

FIG. 8 is a top view of examples of gaps in the conductive layer of thecard.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows the rear side of a memory card exemplifying the presentinvention. The memory card 100 comprises a circuit board 110 having anexposed rear side with terminals 140 and a covered front side (notshown). The covered side comprises at least one integrated circuitincluding flash memory, circuit traces, and passive components, whichare not shown. Cover 120 covers over the front side and edges of thecircuit board, such that the rear side of the circuit board is exposedto form substantially all of the rear side of the memory card. A narrowgap 130 at the junction between the edges of circuit board 110 and cover120 exists. An electrostatic discharge 150 is shown entering the narrowgap 130 at the junction between the edges of circuit board 110 and cover120. U.S. Pat. No. 6,040,622 to Wallace, entitled “Semiconductor PackageUsing Terminals Formed on a Conductive Layer of a Circuit Board”describes in detail the construction of a memory package in detail andis hereby incorporated by reference in its entirety.

FIG. 2 shows the gap 130 between circuit board 110 and cover 120 highlyexaggerated for illustrative purposes. Conductive layers 112 and 114extend to the edge of circuit board 110. The gap is quite small, butlarge enough that an electrostatic discharge (ESD) 150 can reachconductive layer 112 or 114. The conductive layers can be either theground layer or power layer. In the case of an ESD, the ESD will beabsorbed by the conductive layers 112 and 114, rather than by any of thecircuit components on the front side 180 of circuit board 110. The frontside 180 has at least one integrated circuit including flash memory,circuit traces, and passive components.

FIG. 3 shows the bottom of the circuit board 110 with segments 160 of aconductive layer. These segments may be part of circuit traces on thefront side of the circuit board, may be segments that were used forelectroplating purposes on either the front or the back of the circuitboard, or may be test leads that are not needed after a testing or burnin period of the board. During the production of the circuit board, itis cut or sheared to its final dimensions and placed into a plasticcover or encapsulated as seen in FIG. 1. The final shearing or cuttingis performed in a direction from the front side 180 to the rear side 190such that any deformation from the process would extend along edges ofcircuit board 110 from the covered front side 180 down to the exposedrear side 190. Thus for the purposes of describing the relation of thecomponent parts during the shearing or cutting process, the conductivelayers 112 or 114 are described as below the conductive segments 160seen on the covered front side 180 of the circuit board.

FIG. 4 illustrates an intermediate stage in the production of thecircuit board. At this stage, segments 160 are connected to bus 165.Segments 160 and bus 165 are part of the same conductive layer beforecircuit board 180 is trimmed to its final dimensions. The segments inthis intermediate example may be circuit traces used in electroplatingon either the front or back of the circuit board, or as in FIG. 3 may befunctional circuit elements or test leads. The present inventionprotects against short circuiting of any conductive segments of aconductive layer positioned above another conductive layer during acutting or shearing operation.

FIG. 5 a is an enlarged view of an edge of some of the layers of thecircuit board after shearing showing only one gap or slot forillustrative purposes. FIG. 5 a shows conductive layer 112 positionedbelow the conductive segments 160. An insulating layer 116 is positionedbetween the conductive segments 160 and the conductive layer 112.Conductive layer 112 has gaps 112 a and edge portions 112 b. Gaps 112 aare wider (i.e. larger in the X direction) than segments 160 and anydeformation of segments 160 that may reach the plane of conductive layer112 during the shearing or cutting process will arrive at gap 112 arather than contact any portion of the conductive layer 112, thusavoiding a short circuit. Note that edge portions 112 b of circuit board110 are located at the junction 130 between circuit board 110 and cover120 as seen in FIG. 1. Thus a rather large part of the conductive layeris positioned at the edge of the circuit board to attract any ESD whichmay occur, while at the same time any potential short circuit resultingfrom contact of segments 160 with layer 112 or 114 is avoided.

FIG. 6 a is a cross sectional view taken along section A—A of thecircuit board shown in FIG. 5 a. Conductive segment 160 on insulatinglayer 116 has been deformed during the shearing or cutting operationsuch that deformation 160 a of segment 160 extends down the edge of thecircuit board. The amount of deformation and thus size of deformation160 a depend on the shearing force, the geometry of the shearinginstrument, and the elasticity of the metal of the conductive segment.It is foreseen that the deformation may extend down the edge of thecircuit board, i.e. in the Z direction, into or away from the edge ofthe board, i.e. in the Y direction, and across the edge of the board,i.e. in the X direction. Thus the gap 112 a is made sufficiently wideenough that any amount of deformation in the X direction will fall intothe gap and not contact edge portions 112 b. Gap 112 a is alsosufficiently deep enough that any deformation that extends into the gap,or in the Y direction, will likewise not contact conductive layer 112.Conductive layer 114 is fashioned in the same method and has the samestructure as layer 112. Layer 112 or 114 may respectively be either theground or power layer. FIG. 7 shows the relative width, or size of thegap and the segment in the X and Y directions. The size of theconductive segments can vary widely depending on the function of thesegment, but generally range from about one mil (0.001″) up to about 50mils (0.05″), and the width and depth of the gap are sizedproportionally to the segment with sufficient tolerance such that anydeformation will enter the gap and not make contact with the conductivelayer. In one example, the width csw of conductive segment 160 a of FIG.7 is 4 mils wide (i.e. in the X direction), and the width gw of gap 112a is 40 mills from edge to edge (i.e. in the X direction) while thedepth gd is 60 mills (i.e, in the Y direction).

FIG. 5 b is an enlarged view of another example of an edge of thecircuit board. This figure illustrates possible deformation patterns ofsegment 160. Deformation 160 a may extend not only in the Z direction asillustrated by FIG. 5 a, but also laterally along the X axis and intothe gaps 112 a along the Y axis as a result of the trimming of thecircuit board. Gap 112 a is made wide enough (i.e. along the X axis)such that any deformation 160 a will fall into gap 112 a or 114 a andnot make contact with edge portions 112 b of conductive layer 112 or114. Likewise, it is deep enough (i.e. along the Y axis) such that anydeformation into memory card 100 will fall into gap 112 a or 114 a andnot make contact with layer 112 or layer 114. In FIG. 5 b deformations160 a are only shown extending to layer 112. However deformation 160 amay extend to layer 114 and would thus fall into gap 114 a rather thanmake contact with edge portions 114 b.

FIG. 5 c is an enlarged view of another example of an edge of thecircuit board. In this example, all of the layers of the circuit boardare slotted at the edge of the circuit board. A slot 116 c, 112 c, and114 c is formed in insulating layer 116, conductive layer 112, andconductive layer 114 respectively. The slot runs through all of thelayers of the circuit board including the layers that are not shown andthe layers that are not numbered. Slots 116 c, 112 c, and 114 c aresmaller in both the X and Y direction than the gaps 112 a and 114 a inconductive layers 112 and 114. Thus, the gaps 112 a and 114 a extendlaterally (i.e. in the X direction) on either side of slots 112 c and114 c. The gaps 112 a and 114 a also extend deeper (i.e. in the Ydirection) than slots 112 c and 114 c. Thus the slots are formed withinthe gaps and are completely surrounded by the gaps. As with the previousexamples of FIGS. 5 a and 5 b, any deformation 160 a that may occur willfall into gaps 112 a and 114 a rather than make contact with edgeportions 112 b or 114 b of conductive layers 112 and 114. Thus, shortcircuiting is avoided. There can be many different variations in thegeometry of the edge, and in particular the slots 116, 112, and 114 solong the gaps in the conductive layers 112 and 114 are larger in the Xand Y direction than the conductive segments 160 that they are alignedwith.

FIG. 6 b is a cross sectional view taken along section A—A of thecircuit board shown in FIG. 5 c. As described above regarding FIG. 6 a,conductive segment 160 on insulating layer 116 has been deformed duringthe shearing or cutting operation such that deformation 160 a of segment160 extends down the edge of the circuit board. The amount ofdeformation and thus size of deformation 160 a depend on the shearingforce, the geometry of the shearing instrument, and the elasticity ofthe metal of the conductive segment. It is foreseen that the deformationmay extend down the edge of the circuit board, i.e. in the Z direction,into or away from the edge of the board, i.e. in the Y direction, andacross the edge of the board, i.e. in the X direction. Thus the gap 112a is made sufficiently wide enough that any amount of deformation in theX direction will fall into the gap and not contact edge portions 112 bor 114 b. Gap 112 a is also sufficiently deep enough that anydeformation that extends into the gap, or in the Y direction, willlikewise not contact conductive layer 112 or conductive layer 114.

FIG. 8 shows some of the various shapes that gap 112 a may have. Gap 112a may have many different sizes and shapes, all of which areproportionately large enough to avoid any short circuit betweendeformation 160 a and conductive layer 112 or 114.

While an illustrative example of the invention has been shown anddescribed, it will be apparent that other modifications, alterations andvariations may be made by and will occur to those skilled in the art towhich this invention pertains.

It is therefore contemplated that the present invention is not limitedto the embodiments shown and described and that any such modificationsand other embodiments as incorporate those features which constitute theessential features of the invention are considered equivalents andwithin the true spirit and scope of the present invention.

1. A method of making a multi-layer circuit board: forming a firstconductive layer having conductive segments positioned along at leastone edge of the circuit board; forming an insulative layer below thefirst conductive layer forming a second conductive layer below the firstconductive layer and the insulative layer, said second conductive layerhaving gaps positioned along the at least one edge of the circuit board,at least one of said gaps larger than said conductive segments andaligned with said conductive segments; trimming the circuit board andthe conductive segments such that any deformation of the segmentsextends into the gaps and does not make contact with the secondconductive layer.
 2. The method of claim 1 wherein the step of trimmingthe circuit board comprises the step of shearing the circuit board. 3.The method of claim 2 wherein the first conductive layer is shearedbefore the second conductive layer.
 4. A method of making a memorystorage device comprising a circuit board, a cover, and a junctionbetween an edge of the circuit board and the cover comprising: forming afirst metallic layer comprising a first area, a bus, and a plurality ofsegments connecting the first area to the bus at the edge of the circuitboard, the first area positioned within the circuit board, the buspositioned without the circuit board; forming an insulating layer belowthe first area of the first metallic layer; forming a second metalliclayer below the insulating layer and separated from the first metalliclayer by the insulating layer, the second metallic layer extending tothe edge of the circuit board and having a plurality of gaps at the edgeof the circuit board positioned below the plurality of segments;shearing the plurality of segments at the edge of the circuit board andremoving the bus such that any deformation of the segments falls withinthe gaps of the second metallic layer.
 5. The method of claim 4 furthercomprising placing the circuit board into the cover such that the edgeof the circuit board and of the second metallic layer is at the junctionbetween the cover and the circuit board.